Quantum device

ABSTRACT

Disclosed is an electron source  10  including an electron source element  10   a  formed on the side of one surface of an insulative substrate  1 . The electron source element  10   a  includes a lower electrode  2 , a composite nanocrystal layer  6  and a surface electrode  7 . The composite nanocrystal layer  6  includes a plurality of polycrystalline silicon grains  51 , a thin silicon oxide film  52  formed over the surface of each of the grains  51 , a number of nanocrystalline silicons  63  residing between the adjacent grains  51 , and a silicon oxide film  64  formed over the surface of each of the nanocrystalline silicons  63 . The silicon oxide film  64  is an insulating film having a thickness less than the crystal grain size of the nanocrystalline silicon  63 . The surface electrode  7  is formed of a carbon thin film  7   a  laminated on the composite nanocrystal layer  6  while being in contact therewith, and a metal thin film  7   b  laminated on the carbon thin film  7   a.

TECHNICAL FIELD

[0001] The present invention relates to a quantum device utilizing aquantum effect to be induced by electric fields, and more particularlyto an electronic device using nanocrystalline silicons, such as anelectron source adapted to emit electrons based on the electric fieldemission phenomenon or a light-emitting device adapted to emit light inresponse to applied electric fields.

BACKGROUND ART

[0002] In the field of quantum devices, there have heretofore been maderesearch and development on an electronic device using nanocrystallinesilicons, such as an electron source (see, for example, Japanese PatentNo. 2966842) or a light-emitting device (see, for example, JapanesePatent Laid-Open Publication No. H06-90019).

[0003] This type of conventional electron source comprises a lowerelectrode, a surface electrode (upper electrode) formed of a metal thinfilm and disposed in opposed relation to the lower electrode, and astrong electric field drift layer (hereinafter referred to as “driftlayer”) disposed between the lower and surface electrodes. In the driftlayer, electrons drift from the lower electrode toward the surfaceelectrode in response to an electric field acting on the drift layerwhen a voltage is applied between the lower and surface electrodes insuch a manner that the surface electrode has a higher potential thanthat of the lower electrode. In order to allow electrons to be emittedfrom the electron source, a collector electrode is disposed in a vacuumspace to be opposed to the surface electrode. Then, a voltage is appliedbetween the collector electrode and the surface electrode in such amanner that the collector electrode has a higher potential than that ofthe surface electrode while applying a voltage between the lower andsurface electrodes in such a manner that the surface electrode has ahigher potential than that of the lower electrode. In this way,electrons are injected from the lower electrode to the drift layer, andthen emitted through the surface electrode after drifting in the driftlayer.

[0004] The drift layer includes a number of nanocrystalline silicons.The surface-electrode is formed of a metal thin film (e.g. a gold thinfilm) having a thickness of about 10 nm. For example, the lowerelectrode of the conventional electron source is composed of asemiconductor substrate having a conductivity relatively close to thatof conductor, and an ohmic electrode formed on the back surface of thesemiconductor substrate. Alternatively, the lower electrode is composedof an insulative substrate (e.g. a glass substrate having an insulationperformance, a ceramic substrate having an insulation performance etc.),and a conductive layer made of metal material and formed on theinsulative substrate.

[0005] In the conventional light-emitting device, a pair of electrodesare provided, respectively, on both sides in the thickness direction ofa luminescent layer including a number of nanocrystalline silicons. Whena voltage is applied between the electrodes, the luminescent layergenerates light, and the generated light is emitted through one of theelectrode. This electrode is formed of a metal thin film having athickness allowing the light to transmit therethrough. The metal thinfilm of the electron source or the light-emitting device is preparedthrough a sputtering method or the like.

[0006] Generally, it is desired that a metal thin film for use in aquantum device, such as an electron source or light-emitting device, hasa reduced thickness as much as possible. However, if the metal thin filmis thinned, it will have a poor coverage to a base (drift layer orluminescent layer), or will cause agglutination of its components due tosurface tension and other factors, resulting in deteriorated durabilityof the electron source or light-emitting device. Further, in a processof vacuum-sealing the electron source, the metal thin film inevitablyreceives heat. Thus, the heat causes agglutination of the components ofthe metal thin film, and the resultingly lowered coverage to the baseleads to deteriorated durability of the electron source orlight-emitting device.

[0007] As one of solutions to these problems, it is conceivable to makethe metal thin film of chromium having a higher coverage than that ofgold. However, chromium is inherently susceptible to oxidation (or, poorin oxidation resistance). If the metal thin film is oxidized, theresultingly increased electrical resistance thereof will lead todeterioration in electron emission characteristics of the electronsource or the luminescence characteristic of the light-emitting device,and to undesirably increased power consumption. In addition, chromium isstrongly influenced by impurity gas (particularly, oxygen) or waterresiding in the vacuum space, which also leads to deteriorateddurability of the electron source or light-emitting device.

SUMMARY OF THE INVENTION

[0008] In view of the above problems, it is therefore an object of thepresent invention to provide a quantum device, such as an electronsource or a light-emitting device, having enhanced durability ascompared to the conventional quantum devices.

[0009] In order to achieve this object, the present invention provides aquantum device. The quantum device includes a lower electrode, a siliconlayer formed on the lower electrode including a number ofnanocrystalline silicons to induce a quantum effect in response to anelectric field applied thereto, and a carbon thin film formed on thesilicon layer to be in contact with the nanocrystalline silicons.

[0010] In this quantum device, the surface electrode is formed of acarbon thin film which has excellent compatibility with the siliconlayer including a number of nanocrystalline silicons, and highwater-repellency. Thus, as compared to the conventional surfaceelectrode made of metal, the surface electrode formed of the carbon thinfilm can provide enhanced coverage to the silicon layer while preventingaggregation of the components of the surface electrode. In addition, thesurface electrode can prevent impurities such as oxygen or water frombeing mixed into the silicon layer. Furthermore, the surface electrodecan have enhanced adhesion to the silicon layer as well as enhanced heatresistance and oxidation resistance. By virtue of these enhancedproperties, the quantum device of the present invention can have morestable quantum effect and enhanced durability as compared to theconventional quantum devices.

[0011] The term “in contact with nanocrystalline silicons” herein is notlimited to the state where nanocrystalline silicons and carbons are indirect contact with each other, but the state where nanocrystallinesilicons are in indirect contact with carbons through a natural oxidefilm formed on the nanocrystalline silicons, or an insulating film suchas an oxide film, nitride film or oxynitride film formed thenanocrystalline silicons by use of oxidizing means or nitriding means.Because, it is practically difficult to prevent formation of the naturaloxide film during handling due to extremely high activity of the surfaceof the nanocrystalline silicon, or the insulating film is formed on thenanocrystalline silicon in some devices.

[0012] The quantum device of the present invention may further include ametal thin film formed on the carbon thin film. In this case, the metalthin film may be made of a material selected from the group consistingof gold, platinum, silver, copper, hafnium, zirconium, titanium,tantalum, iridium, niobium, chromium, aluminum, and carbide or nitridethereof.

[0013] In the quantum device of the present invention, the carbon thinfilm may be made of graphite or graphite-like carbon. In this case, theelectrical resistance of the carbon thin film can be reduced as comparedto a carbon thin film made of amorphous carbon or diamond-like carbon.Thus, a required driving voltage and power consumption can be reducedwhile suppressing undesirable affects from heat generation or voltagedrop in the carbon thin film.

[0014] In the quantum device of the present invention, the carbon thinfilm may have a conducting property yielded by doping an impuritytherein. In this case, the electrical resistance of the carbon thin filmcan be reduced as compared to a non-doped carbon thin film. Thus, arequired driving voltage and power consumption can be reduced whilesuppressing undesirable affects from heat generation or voltage drop inthe carbon thin film.

[0015] In the quantum device of the present invention, the carbon thinfilm may have a thickness of 5 nm or less. For example, if the quantumdevice is an electron source, the deterioration in electron emissionefficiency can be suppressed. If the quantum device is a light-emittingdevice, the deterioration in optical output can be suppressed.

[0016] Further, in this carbon thin film, the lower limit of thethickness may be 1 nm or more (while setting the upper limit of thethickness at 5 nm or less). In this case, the carbon thin film canstably achieve the above effect. More specifically, if the surfaceelectrode is formed of only the carbon thin film, the thickness of thecarbon thin film may have a lower limit of 3 nm or more. If the surfaceelectrode is formed of the carbon thin film and the metal thin film, thethickness of the carbon thin film may have an upper limit of 3 nm orless.

[0017] In the quantum device of the present invention, the carbon thinfilm may be a film formed under a temperature of 250° C. or more. Inthis case, any water absorbed in the silicon layer can be removed byheating (at 250° C. or more under vacuum) the silicon layer before theformation of the carbon thin film, to provide enhanced characteristicsand stability of the quantum device. The carbon thin film can be formedin succession to the completion of the removal of the water, to keep thesilicon layer from water while preventing water from being re-absorbedtherein when the quantum device is taken out into atmosphere after thefilm formation (capping effect), so as to provide more enhancedstability of the quantum device. While the above effect may be obtainedby removing water in the silicon layer through a heat treatment in aprocess precedent to the formation of the carbon thin film, the siliconlayer including a number of nanocrystalline silicons would easilyre-absorb water when it is taken out into atmosphere after the heattreatment, due to its high ability of absorbing water therein. Thus, theformation of the carbon thin film under a temperature of 250° C. or moreallows the carbon thin film to be formed on the silicon layer afterremoving water therefrom, so as to perform an effective water-removingoperation.

[0018] If the surface electrode is formed of only the carbon thin film,the quantum device of the present invention may be subjected to a heattreatment after the carbon thin film is formed therein and before theelectric field is applied thereto. If the surface electrode is formed ofthe carbon thin film and the metal thin film, the quantum device may besubjected to a heat treatment after the carbon thin film and the metalthin film are formed therein and before the electric field is appliedthereto. In this case, the carbon thin film can have enhanced filmquality to provide enhanced stability and heat resistance of the quantumdevice. For example, in an electron source, it is fundamentally requiredto have a heat resistance against about 400° C. which is necessary for avacuum-sealing process using frit glass. Thus, the heat treatment shouldbe performed at a temperature close to 400° C. If the temperature isexcessively lower than 400° C., the film quality will not besufficiently improved. If the temperature is excessively higher than400° C., the carbon thin film or the metal thin film will be damaged.Thus, it is desirable to perform the heat treatment at a temperature of380 to 420° C.

[0019] The quantum device of the present invention may serve (may beused) as an electron source by arranging the silicon layer as astrong-field drift layer capable of accelerating an electrode based on astrong electric field effect. In this case, the silicon layer may be acomposite nanocrystal layer which includes a polycrystalline silicon,and a number of nanocrystalline silicons residing around the grainboundary of the polycrystalline silicon. The quantum device of thepresent invention may also serve (may also be used) as a light-emittingdevice by arranging the silicon layer as a luminescent layer capable ofemitting light in response to an electric field applied thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be more sufficiently understood fromthe detailed description and the accompanying drawings. In theaccompanying drawings, common components or elements are defined by thesame reference numerals or codes.

[0021]FIG. 1A is a vertical sectional view of an electron sourceaccording to the present invention. FIG. 1B is a schematic fragmentaryenlarged view of the electron source in FIG. 1A.

[0022]FIG. 2 is an explanatory diagram of an electron emission operationof the electron source in FIG. 1A.

[0023]FIGS. 3A to 3D are sectional views of an electron source andintermediate products in a production process of the electron source,which show a production method of the electron source according to thepresent invention.

[0024]FIG. 4 is a graph showing respective aging characteristics ofdiode current and emission current in an electron source according tothe present invention.

[0025]FIG. 5 is a graph showing respective aging characteristics ofdiode current and emission current in an electron source according tothe present invention.

[0026]FIG. 6 is another graph showing respective aging characteristicsof diode current and emission current in an electron source according tothe present invention.

[0027]FIGS. 7A and 7B are graphs showing respective agingcharacteristics of diode current, emission current and electron emissionefficiency, wherein FIG. 7A shows the characteristics in an electronsources including a carbon thin film having a thickness of 0.5 nm, andFIG. 7B shows the characteristics in an electron sources including acarbon thin film having a thickness of 1.0 nm.

[0028]FIG. 8 is a graph showing the relationship between desorbed watercontent and temperature when a silicon layer used in an electron sourceaccording to the present invention is heated.

[0029]FIGS. 9A and 9B are graphs showing heat resistance in an electronsource subjected to no heat treatment before an electric field isapplied thereto. FIGS. 9C and 9D are graphs showing heat resistance inan electron source subjected to a heat treatment before an electricfield is applied thereto.

[0030]FIG. 10A is a vertical sectional view of a light-emitting deviceaccording to the present invention. FIG. 10B is a schematic fragmentaryenlarged view of the light-emitting device in FIG. 10A.

[0031]FIGS. 11A to 11D are sectional views of a light-emitting deviceand intermediate products in a production process of the light-emittingdevice, which show a production method of the light-emitting deviceaccording to the present invention.

[0032]FIG. 12 shows a graph showing respective change characteristics ofcurrent density and electroluminescence intensity with respect tovoltage in a light-emitting device according to the present invention.

[0033]FIG. 13 shows a graph showing respective aging characteristics ofcurrent density and electroluminescence intensity in a light-emittingdevice according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0034] This application is based upon and claims the benefit of priorityfrom the prior Japanese Patent Application No. 2002-064287, the entirecontents of which are incorporated herein by reference.

[0035] With reference to the accompanying drawings, several embodimentsof the present invention will now be specifically described. Memberscommon in each embodiment or members having substantially the samestructure and function are defined by the same reference numerals, andduplicate descriptions will be fundamentally omitted.

[0036] (First Embodiment)

[0037] A first embodiment of the present invention will be describedbelow. A quantum device according to the first embodiment is an electronsource adapted to emit electrons based on electric fields appliedthereto, as one of electronic devices utilizing nanocrystallinesilicons.

[0038] As shown in FIG. 1A, the electron source 10 according to thefirst embodiment includes an electron source element 10 a formed on theside of one surface of an insulative substrate 1 (e.g. a glass substratehaving an insulation performance or a ceramic substrate having aninsulation performance). The electron source element 10 a includes alower electrode 2 formed on the side of the above surface of theinsulative substrate 1, a composite nanocrystal layer 6 formed on thelower electrode 2, and a surface electrode 7 formed on the compositenanocrystal layer 6. As described in detail later, the compositenanocrystal layer 6 includes a polycrystalline silicon, and a number ofnanocrystalline silicons residing around the grain boundary of thepolycrystalline silicon.

[0039] In the electron source element 10 a, the surface electrode 7 isopposed to the lower electrode 2, and the composite nanocrystal layer issandwiched between the surface electrode 7 and the lower electrode 2.The thickness of the lower electrode 2 is set at about 300 nm (e.g. 330nm), and the thickness of the surface electrode 7 is set at about 10 nm.The lower electrode 2 is formed of a single-layer or multilayer metalthin film made of metal material (e.g. elemental metal such as Cr, W,Ti, Ta, Ni, Al, Cu, Au, Pt or Mo; alloy thereof; or intermetalliccompound such as silicide). The composite nanocrystal layer 6 is formedby subjecting a polycrystalline silicon to a nanocrystallization processand an oxidation process.

[0040] As shown in FIG. 1B, the composite nanocrystal layer 6 includes aplurality of polycrystalline silicon grains 51, a thin silicon oxidefilm 52 formed over the surface of each of the grains 51, the number ofnanocrystalline silicons 63 residing between the adjacent grains 51, anda silicon oxide film 64 formed over the surface of each of thenanocrystalline silicons 63. The silicon oxide film 64 is an insulatingfilm having a thickness less than the crystal grain size of thenanocrystalline silicon 63. It is believed that the remaining region ofthe composite nanocrystal layer 6 other than the grains 51, thenanocrystalline silicons 63 and the silicon oxide films 52, 64 is anamorphous region 65 of amorphous silicon or partially oxidized amorphoussilicon.

[0041] That is, the composite nanocrystal layer 6 includes thepolycrystalline silicon, and the number of nanocrystalline silicons 63residing around the grain boundary of the polycrystalline silicon. Eachof the grains 51 extends in the thickness direction of the lowerelectrode 2. In the first embodiment, a plurality of compositenanocrystal layers 6 serve as a drift layer (strong electric field driftlayer).

[0042] The surface electrode 7 is formed of a carbon thin film 7 adeposited (laminated) on the composite nanocrystal layer 6, and a metalthin film 7 b deposited on the carbon thin film 7 a. The carbon thinfilm 7 a is in contact with the nanocrystalline silicons 63 through therespective silicon oxide films 64 formed over the surface of thenanocrystalline silicons 63. As mentioned above, in this specification,the state where the carbon thin film 7 a is in indirect contact with thenanocrystalline silicons 63 through the silicon oxide films 64 is alsodescribed herein by using the expression “the carbon thin film 7 a is incontact with the nanocrystalline silicons 63”. In view of suppressingthe deterioration of electron emission efficiency, the thickness of thecarbon thin film 7 a in the surface electrode 7 is set in the range of 1nm to 5 nm. Further, the total thickness of the carbon thin film 7 a andthe metal thin film 7 b is arranged at about 10 nm.

[0043] Since the carbon thin film 7 a is made of carbon belonging toGroup IV elements as with silicon which is a primary component of thecomposite nanocrystal layer 6 serving as a base thereof, it hasexcellent compatibility with the composite nanocrystal layer 6, and highwater-repellency. The carbon thin film 7 a can also provide excellentcoverage while facilitating reduction in film thickness, and preventimpurities such as oxygen or water from being mixed into the compositenanocrystal layer 6. In addition, the carbon thin film 7 a has excellentadhesion with the composite nanocrystal layer 6 as well as excellentheat resistance and oxidation resistance.

[0044] The carbon thin film 7 a may be formed of various types of carbonmaterial such as amorphous carbon, graphite, graphite-like carbon,diamond or diamond-like carbon. If graphite or graphite-like carbon isused, the electrical resistance of the carbon thin film 7 a will bereduced as compared to the carbon thin film made of amorphous carbon,diamond or diamond-like carbon. Thus, a required driving voltage andpower consumption can be reduced while suppressing undesirable affectsfrom heat generation or voltage drop in the carbon thin film 7 a.Further, if an impurity is doped into the carbon thin film 7 a toprovide a conducting property therein, the electrical resistance of thecarbon thin film 7 a will be reduced as compared to a non-doped carbonthin film. Thus, a required driving voltage and power consumption can bereduced while suppressing undesirable affects from heat generation orvoltage drop in the carbon thin film 7 a.

[0045] Preferably, the metal thin film 7 b is made of a material havingrelatively high conductivity, relatively low work function, excellentoxidation resistance and chemical stability. Such a material includesgold, platinum, silver, copper, hafnium, zirconium, titanium, tantalum,iridium, niobium, chromium, aluminum, and tungsten. Carbide or nitrideof these metals may also be used. The metal thin film 7 a made of thesematerials can have enhanced adhesion with the carbon thin film 7 a toprovide an improved yield ratio in the production process of theelectron source.

[0046] As shown in FIG. 2, in order to allow electrons to be emittedfrom the electron source element 10 a, a collector electrode 9 isdisposed in opposed relation to the surface electrode 7. Then, the spacebetween the surface electrode 7 and the collector electrode 9 ismaintained in vacuum, and a DC voltage Vps is applied between thesurface electrode 7 and the lower electrode 2 in such a manner that thesurface electrode 7 has a higher potential than that of the lowerelectrode 2. Further, a DC voltage Vc is applied between the collectorelectrode 9 and the surface electrode 7 in such a manner that thecollector electrode 9 has a higher potential than that of the surfaceelectrode 7. The DC voltages Vps, Vc can be adequately set to allowelectrons injected into the lower electrode 2 to be emitted through thesurface electrode 7 after drifting in the composite nanocrystal layer 6(one-dot chain lines in FIG. 2 indicate the flow of electrons e⁻ emittedthrough the surface electrode 7). It is believed that the electronsreaching the surface of the composite nanocrystal layer 6 are hotelectrons, and such electrons are emitted to the vacuum space afterreadily tunneling through the surface electrode 7. In short, an electricfield acting on the composite nanocrystal layer 6 when the surfaceelectrode 7 has a higher potential than that of the lower electrode 2allows electrons to drift from the lower electrode 2 toward the surfaceelectrode 7.

[0047] Generally, in this type of electron source element 10 a, acurrent flowing between the surface electrode 7 and the lower electrode2 is referred to as “diode current Ips”, and a current flowing betweenthe collector electrode 9 and the surface electrode 7 is referred to as“emission current (emission electron current) Ie” (see FIG. 2). Theelectron emission efficiency (=(Ie/Ips)×100 [%]) is increased as theratio of emission current Ie to diode current Ips (=Ie/Ips) isincreased. Even if the DC voltage Vps to be applied between the surfaceelectrode 7 and the lower electrode 2 is in a low range of about 10 to20 V, the electron source 10 according to the present invention can emitelectrons. Thus, the vacuum dependence of electron emissioncharacteristics can be reduced so as to allow electrons to be stablyemitted without occurrence of a so-called popping phenomenon.

[0048] It is believed that electrons are emitted from the electronsource element 10 a in the following model. The DC voltage Vc is appliedbetween the collector electrode 9 and the surface electrode 7 in such amanner that the collector electrode 9 has a higher potential than thatof the surface electrode 7 while applying the DC voltage Vps between thesurface electrode 7 and the lower electrode 2 in such a manner that thesurface electrode 7 has a higher potential than that of the lowerelectrode 2.

[0049] Electrons e⁻ are thermally excited, and injected from the lowerelectrode 2 into the composite nanocrystal layer 6. When the DC voltageVps is applied to the composite nanocrystal layer 6, most of thegenerated electric field acts on the silicon oxide films 64. Thus, theelectrons e⁻ injected into the composite nanocrystal layer 6 isaccelerated by the strong electric field acting on the silicon oxidefilms 64 to drift in the region of the composite nanocrystal layer 6between the grains toward the surface electrode 7 in the direction ofthe arrows at the center of FIG. 1B. When the DC voltage Vps goes up toa predetermined value (e.g. a potential equal to or greater than thework function of the metal thin film 7 b of the surface electrode 7),the electrons e⁻ tunneling through the surface electrode 7 are emittedto the vacuum space. In this process, the electrons e⁻ tunnel throughthe nanocrystalline silicons 63 without scattering because each of thenanocrystalline silicons 63 has a size approximately equal to a Bohrradius. Thus, the electrons e⁻ accelerated by the strong electric fieldacting on the thin silicon oxide films 64 formed over the respectivenanocrystalline silicons are emitted through the surface electrode 7after drifting in the composite nanocrystal layer 6 without scattering.

[0050] Since heat generated in the composite nanocrystal layer 6 isreleased through the grains 5, the electrons can be stably emitted fromthe composite nanocrystal layer 6 without occurrence of the poppingphenomenon during the electron emission operation. In addition, theelectrons reaching the surface of the composite nanocrystal layer 6 areemitted to the vacuum space after readily tunneling through the surfaceelectrode 7 because they would be hot electrons as mentioned above.

[0051] The electron source element 10 a operable based on the aboveprinciple is generally referred to as “Ballistic electronSurface-emitting Device”.

[0052] In the electron source 10 according to the first embodiment, thesurface electrode 7 is formed of the carbon thin film 7 a havingexcellent compatibility with the composite nanocrystal layer 6 servingas a base thereof and high water-repellency, and the metal thin film 7b. The carbon thin film 7 a can provide excellent coverage whilefacilitating reduction in film thickness, and prevent impurities such asoxygen or water from being mixed into the composite nanocrystal layer 6.In addition, the carbon thin film 7 a has excellent adhesion with thecomposite nanocrystal layer 6 as well as excellent heat resistance andoxidation resistance. Thus, the electron source 10 can prevent orsuppress the conventional problems such as the peeling of the surfaceelectrode 7 from the composite nanocrystal layer 6, the aggregation ofthe components of the surface electrode 7 and the oxidation of thesurface electrode 7. Therefore, as compared to the conventional electronsource having the surface electrode formed of only the metal electrode,the electron source 10 according to the first embodiment can haveenhanced durability while suppressing deterioration in electron emissionefficiency.

[0053] With reference to FIGS. 3A to 3D, a production method of theelectron source 10 according to the first embodiment will be describedbelow. In the production process of the electron source 10, a lowerelectrode 2 in the form of a laminate film formed by depositing(laminating) first and second metal layers deposited to have a giventhickness (for example, a laminate film formed by depositing first andsecond metal layers to have a thickness of 330 nm, wherein the firstmetal layer is made of titanium to have a thickness of 80 nm, and thesecond metal layer is made of tungsten to have a thickness of 250 nm) isfirst formed on the side of one surface of an insulative substrate 1.Then, a non-doped polycrystalline silicon layer 3 having a giventhickness (e.g. 1.5 μm) is formed on the lower electrode 2 to provide astructure as shown in FIG. 3A. The lower electrode 2 may be formed, forexample, through a sputtering method or a vapor deposition method. Thepolycrystalline silicon layer 3 may be formed, for example, through aCVD method (LPCVD method, plasma CVD method, catalytic-CVD method etc.),a sputtering method, a CGS (Continuous Grain Silicon) method, or amethod of depositing amorphous silicon and then laser-annealing theamorphous silicon.

[0054] After the formation of the non-doped polycrystalline siliconlayer 3, a composite nanocrystal layer 4 including polycrystallinesilicon grains 51, nanocrystalline silicons 63 and amorphous silicon isformed through a nanocrystallization process to provide a structure asshown in FIG. 3B.

[0055] The nanocrystallization process is performed by using aprocessing bath containing an electrolytic solution which is a mixtureprepared by mixing a water solution containing 55 wt % of hydrogenfluoride with ethanol at a ratio of about 1:1. In the processing bath, agiven voltage is applied between a platinum electrode (not shown) andthe lower electrode 2. The composite nanocrystal layer 4 is formed bysupplying a given constant current to the polycrystalline silicon layer3 while irradiating it with light.

[0056] After the completion of the nanocrystallization process, acomposite nanocrystal layer 6 having the structure as shown in FIG. 1Bis obtained through an oxidation process to provide a structure as shownin FIG. 3C. The oxidation process is performed by using anoxidation-processing bath containing an electrolytic solution (e.g. 1mol/l of H₂SO₄, 1 mol/l of HNO₃, aqua regia etc.). In the oxidationbath, a given voltage is applied between a platinum electrode (notshown) and the lower electrode 2 to electrochemically oxidize thecomposite nanocrystal layer 4. Through this process, the compositenanocrystal layer 6 including the grains 51, the nanocrystallinesilicons 63, and the silicon oxide films 52, 62 is formed. The oxidationprocess is not limited to the electrochemical oxidation process, but anyother suitable oxidation process such as a rapid-heating oxidationprocess may be used.

[0057] After the formation of the composite nanocrystal layer 6, acarbon thin film 7 a and a metal thin film 7 b are formed in turn, and asurface electrode 7 in the form of a laminate film formed by depositing(laminating) the carbon thin film 7 a and the metal thin film 7 b isformed on the composite nanocrystal layer 6 to provide an electronsource 10 having a structure as shown in FIG. 3D. While the carbon thinfilm 7 a may be formed through various thin-film forming methods, suchas a vapor deposition method, a sputtering method, an ion platingmethod, a thermal CVD method or a PECVD method, it is understood that athin-film forming method capable of forming a thin film having even filmthickness and excellent coverage should be used. The metal thin film maybe formed through various thin-film forming methods, such as a vapordeposition method, a sputtering method, an ion plating method or a CVDmethod.

[0058] The above electron-source production method allows an electronsource 10 to be produced at a high yield rate while suppressingdeterioration in electron emission efficiency and improving durability.

[0059] As described above, in the first embodiment, the compositenanocrystal layer 6 includes the silicon oxide films 52, 64 in additionto the polycrystalline silicon grains 51 and the nanocrystallinesilicons 63. However, a silicon nitride film or silicon oxynitride filmmay be included as a substitute for the silicon oxide films 52, 64. Inthis case, instead of the oxidation process, a nitriding process or anoxynitriding process may be used.

[0060] If the electron source 10 according the first embodiment is usedas an electron source for displays, a number of electron source elements10 a may be prepared by appropriately patterning the lower electrode 2,the surface electrode 7 and the composite nanocrystal layer 6, and thenarranged on the side of one surface of the insulative substrate 1 in amatrix pattern. Further, in the first embodiment, the surface electrode7 is composed of the laminate film consisting of the carbon thin film 7a and the metal thin film 7 b. However, the surface electrode 7 may beformed of only the carbon thin film 7 a.

[0061] (Example of First Embodiment)

[0062] An electron source 10 as a first example was produced inaccordance with the production method according to the first embodiment,and respective aging characteristic of diode current Ips and emissioncurrent Ie in the electron source 10 were measured. The measurementresult is shown in FIG. 4. In the first example, an insulative substrate1 is a glass substrate. A lower electrode 2 is a laminate filmconsisting of a titanium layer having a thickness of 80 nm and atungsten layer having a thickness of 250 nm, which were formed through asputtering method.

[0063] In the first example, a non-doped polycrystalline silicon layer 3(see FIG. 3A) was formed through a plasma CVD method to have a thicknessof 1.5 μm. The nanocrystallization process was performed by using anelectrolytic solution prepared by mixing a water solution containing 55wt % of hydrogen fluoride with ethanol at a ratio of about 1:1. In theelectrolytic solution cooled down to 0° C., a constant current of 25mA/cm² from a power supply was supplied between the lower electrode 2serving as an anode and a platinum electrode serving as a cathode for 8seconds while irradiating the principal surface of the polycrystallinesilicon layer 3 with light by using a 500 W tungsten lump as a lightsource. An electrochemical oxidation process was used as the oxidationprocess. In an oxidation-processing bath containing 1 mol/l of H₂SO₄, avoltage of 27 V was applied between a platinum electrode (not shown) andthe lower electrode 2.

[0064] A surface electrode 7 is a laminate film consisting of a carbonthin film 7 a having a thickness of 2 nm and a gold thin film having athickness of 10 nm which were formed through a sputtering method.

[0065] In measuring diode current Ips and emission current Ie, theelectron source 10 was first introduced in a vacuum chamber (not shown),and a collector electrode 9 was disposed in opposed relation to thesurface electrode 7 (see FIG. 2). Then, a DC voltage Vc was applied insuch a manner that the collector electrode 9 has a higher potential thanthat of the surface electrode 7 while applying a DC voltage Vps in sucha manner that the surface electrode 7 has a higher potential than thatof the lower electrode 2.

[0066]FIG. 4 shows the measurement result of electron emissioncharacteristics on the condition that a vacuum in the vacuum chamber is1×10-3 Pa, and the DC current Vps is 19 V. In FIG. 4, the horizontalaxis represents a lapsed time, and the vertical axis represents acurrent density. Further, a indicates an aging characteristic of thecurrent density of diode current Ips, and β indicates an agingcharacteristic of the current density of emission current Ie. As seen inFIG. 4, the electron source 10 of the first example exhibited anexcellent aging characteristic in both the diode current Ips and theemission current Ie.

[0067]FIG. 5 shows respective aging characteristics of diode current Ipsand emission current Ie in an emission source 10 of a second example andan electron source of a comparative example. In FIG. 5, the horizontalaxis represents a lapsed time, the vertical axis on the left siderepresenting a current density of diode current Ips, and the verticalaxis on the right side representing a current density of emissioncurrent Ie. Further, α indicates an aging characteristic of the currentdensity of diode current Ips in the electron source 10 of the secondexample, β indicating an aging characteristic of the current density ofemission current Ie in the electron source 10 of the second example, γindicating an aging characteristic of the current density of diodecurrent Ips in the electron source of the comparative example, and δindicating an aging characteristic of the current density of emissioncurrent Ie in the electron source of the comparative example.Differently from the electron source in FIG. 4, the electron source 10of the second example used in the measurement of FIG. 5, a voltage of 32V was applied in the oxidation process. The electron source ofcomparative example has a surface electrode formed of a gold thin film.

[0068] As seen in FIG. 5, the electron source 10 of the second exampleusing the surface electrode 7 formed of the laminate film consisting ofthe carbon thin film 7 a and the metal thin film 7 b exhibited anexcellent aging characteristic of the emission current Ie, as comparedto the comparative example having the surface electrode formed of onlythe metal thin film. That is, it is proved that the electron source 10of the second example provides enhanced aging characteristics in theemission current Ie and the electron emission efficiency, as compared tothe comparative example.

[0069]FIG. 6 shows respective aging characteristics of diode current Ipsand emission current Ie in an electron source 10 which is different fromthe electron source concerning FIG. 4 in terms of the conditions of thenanocrystallization process and the oxidation process. In thenanocrystallization process for the electron source 10 concerning FIG.6, a cycle consisting of a low current period for supplying a current of2.5 MA/cm² for 2 seconds and a high current period for supplying acurrent of 25 mA/cm² for 4 seconds was repeated three times. Further, arapid-heating oxidation process was used as the oxidation process. Theelectron source 10 concerning FIG. 6 exhibited an excellent stabilityagainst aging as with the electron source of the first example in FIG.4.

[0070] In the electron source 10 of the present invention, the thicknessof the carbon thin film 7 a is set at 1 nm or more, and thus the carbonthin film can be stably introduced.

[0071]FIGS. 7A and 7B show the stability of electron emissioncharacteristics or the stability of diode current Ips, emission currentIe and electron emission efficiency of the electron source 10, whereinFIG. 7A shows the characteristics in an electron sources including acarbon thin film 7 a having a thickness of 0.5 nm, and FIG. 7B shows thecharacteristics in an electron sources including a carbon thin film 7 ahaving a thickness of 1.0 nm. As seen in FIGS. 7A and 7B, while thecarbon thin film 7 a having a thickness of 1 nm provides a stableelectron emission characteristic, the electron emission characteristicis significantly deteriorated in the carbon thin film 7 a having athickness of 0.5 nm. The reason of this deterioration would be assumedthat carbons constituting the carbon thin film 7 a grow in an islandshape without forming a complete film when the thickness is 0.5 nm. Thereason would also be assumed that even if a film is fully formed, asufficient effect cannot be obtained due to excessively thin filmthickness. Thus, when the surface electrode 7 is formed of the carbonthin film 7 a and metal thin film 7 b, it is desired to set thethickness of the carbon thin film 7 a at 3 nm or less so as to reducethe film thickness of the surface electrode 7. On the other hand, whenthe surface electrode 7 is formed of only the carbon thin film 7 awithout the metal thin film 7 b, it is desired to set the thickness ofthe carbon thin film 7 a at 3 nm or more so as to suppress increase inelectrical resistance. This condition is not limited to the electronsource 10, but can also be applied to other quantum device such as alight-emitting device.

[0072] If the carbon thin film is formed under 250° C. or more, theelectron source element can have enhanced characteristics or stability.

[0073]FIG. 8 shows the relationship between desorbed water content andtemperature when the temperature of a silicon layer is increased todesorb water in the silicon layer (through Thermal DesorptionSpectrometroy). In FIG. 8, the amount of desorbed water is representedby the value of ion current in proportion thereto. As shown in FIG. 8,some peaks of desorbed water amount can be found in the temperaturerange of 250° C. or less. At these peaks, water absorbed in the siliconlayer is desorbed. Thus, the composite nanocrystal layer 6 (siliconlayer) can be heated at 250° C. in vacuum before the formation of thecarbon thin film 7 a, to remove water absorbed in the compositenanocrystal layer 6 so as to provide enhanced characteristics orstability of the electron source element.

[0074] Further, the carbon thin film 7 a can be formed in succession tothe completion of the removal of the water in the composite nanocrystallayer 6 by heating or warming, to keep the composite nanocrystal layer 6from water while preventing water from being re-absorbed therein whenthe quantum device is taken out into atmosphere after the formation ofthe carbon thin film 7 a (capping effect), so as to provide moreenhanced characteristics or stability of the electron source element 10a. While the above effect may also be obtained by removing the waterthrough a heat treatment in a process precedent to the formation of thecarbon thin film, the composite nanocrystal layer (silicon layer)including the number of nanocrystalline silicons would easily re-absorbwater when an electron-source intermediate product is taken out intoatmosphere after the heat treatment, due to its high ability ofabsorbing water therein. Thus, the formation of the carbon thin film 7 aunder a temperature of 250° C. or more allows the carbon thin film to beformed on the composite nanocrystal layer after removing watertherefrom, so as to perform an effective water-removing operation. Thisoperation is not limited to the electron source 10, but can also beapplied to other quantum device such as a light-emitting device. In thisoperation, the carbon thin film may be formed after heating thecomposite nanocrystal layer 6 (silicon layer) at 250° C. or more toremove water therefrom, and then cooling the substrate down to roomtemperature.

[0075] In the production process of the electron source 10, the electronsource 10 may be subjected to a heat treatment after the carbon thinfilm 7 a and the metal thin film 7 b are formed therein and before theelectric field is applied to the electron source 10, to provide enhancedstability and heat resistance of the electron source element 10 a or theelectron source 10.

[0076]FIGS. 9A to 9D show difference in heat resistance betweenheat-treated and non-heat-treated electron sources.

[0077]FIG. 9A shows electron emission characteristics measured under thecondition that an electric field is applied to the electron source 10after the formation of the electron source element 10 a. FIG. 9B showselectron emission characteristics re-measured after the electron source10 which has been applied with the electric field is subjected to a heattreatment under N₂ atmosphere at 400° C. just for 1 hour. As seen inFIGS. 9A and 9B, the deterioration of the emission current Ie shows thatthe electron source is damaged.

[0078]FIG. 9C shows electron emission characteristics measured under thecondition that the electron source 10 is subjected to a heat treatmentunder N₂ atmosphere at 400° C. just for 1 hour after the electron sourceelement 10 a is formed and before an electric field is applied to theelectron source 10, and then an electric field is applied to theelectron source 10. The characteristics in FIG. 9C are approximately thesame as those in FIG. 9A.

[0079]FIG. 9D shows electron emission characteristics measured under thecondition that the electron source 10 subjected to the heat treatment inFIG. 9C is re-subjected to a heat treatment under N₂ atmosphere at 400°C. just for 1 hour, and then an electric field is applied to theelectron source 10. As seen in FIGS. 9C and 9D, the characteristics inFIG. 9D are approximately the same as those in FIG. 9C, which shows thatthe electron source is not damaged. That is, the electron source 10 hasa heat resistance against 400° C.

[0080] If an electric field is applied to a non-heat-treated electronsource 10, the electron source 10 will be damaged after heat treatment,because the carbon thin film 7 a unstable in film quality damage wouldbe damaged by electrons (quanta) passing therethrough. Thus, theelectron source 10 should be subjected to heat treatment before applyingan electric field to the electron source 10, to provide enhanced filmquality of the carbon thin film 7 a and improved heat resistance of theelectron source 10. If the surface electrode 7 is formed of only thecarbon thin film 7 a, the electron source 10 may be subjected to a heattreatment after the carbon thin film 7 a is formed therein and beforethe electric field is applied to the electron source 10. In this way,the electron source element 10 a or the electron source 10 can haveenhanced stability and heat resistance as with the above case. Thisoperation is not limited to the electron source 10, but can also beapplied to other quantum device such as a light-emitting device.

[0081] From a practical standpoint, the heat resistance against 400° C.is one of critical characteristics for the electron device 10 because itis requited, for example, for a vacuum-sealing process using frit glass.Thus, the heat treatment should be performed at a temperature close to400° C. If the temperature is excessively lower than 400° C., the filmquality will not be sufficiently improved. If the temperature isexcessively higher than 400° C., the carbon thin film 7 a or the metalthin film 7 b will be damaged. Thus, it is desirable to perform the heattreatment at a temperature of 380 to 420° C.

[0082] More specifically, the above heat treatment or the formation ofthe surface electro rode 7 can be performed, for example, by thefollowing process. It is understood that this process is not limited toproduction of the electron source 10, but can also be applied toproduction of other quantum device such as a light-emitting device.

[0083] As with the above example, a lower electrode 2 made of metal isfirst formed on an insulative substrate 1 formed of a glass substrate.Then, a polycrystalline silicon layer 3 is formed on the lower electrode2, for example, through a plasma CVD. The polycrystalline silicon layer3 is subjected to a nanocrystallization process based on anodicoxidation, and a composite nanocrystal layer 6 is formed by creatingoxide films therein through an electrochemical oxidation process.

[0084] Then, a carbon thin film 7 a is formed through a sputteringprocess. In this process, an electron-source intermediate product isheated up to 250° C. under a vacuum of 1×10⁻⁵ Pa or less to form acarbon thin film 7 a having a thickness of 1 nm. During this process,the vacuum is once reduced due to desorption of water from the compositenanocrystal layer 6 which is heated or warmed. After substantially theentire water in the composite nanocrystal layer 6 is desorbed therefrom,the vacuum returns to the original value before heating. Then, thecarbon thin film 7 a is formed to have a thickness of 1 nm. After theformation of the carbon thin film 7 a, the temperature is reduced whilemaintaining the vacuum to form a Cr layer having a thickness of 2 nm andan Au layer having a thickness of 8 nm. Then, the electron source 10 issubjected to a heat treatment under N₂ atmosphere at 400° C. just 1 hourbefore an electric field is applied to the electron source 10.

[0085] (Second Embodiment)

[0086] A second embodiment of the present invention will be describedbelow. A quantum device according to the second embodiment is alight-emitting device adapted to emit light based on electric fieldapplied thereto, as one of electronic devices utilizing nanocrystallinesilicons.

[0087] As shown in FIG. 10A, the light-emitting device 20 according tothe second embodiment comprises an n-type silicon substrate 21, and anohmic electrode 22 formed on the back surface of the n-type siliconsubstrate 21. A luminescent layer 26 having a number of nanocrystallinesilicons 63 (see FIG. 10B) is formed on the front surface of the siliconsubstrate 21, and an upper electrode 27 is formed on the luminescentlayer 26. In this light-emitting device 20, a lower electrode 25 iscomprised of the silicon substrate 21 and the ohmic electrode 22. Theluminescent layer 26 is sandwiched between the lower electrode 25 andthe upper electrode 27. More specifically, the lower electrode 25 isdisposed on one side in the thickness direction of the luminescent layer26, and the upper electrode 27 is disposed on the other side, so thatthe lower electrode 25 and the upper electrode 27 act as a pair ofelectrodes. In this light-emitting device 20, light generated in theluminescent layer 26 is output outside through the upper electrode 27.The thickness of the upper electrode 27 is set at about 10 nm.

[0088] The luminescent layer 26 is formed by subjecting apolycrystalline silicon layer or a silicon layer to ananocrystallization process and an oxidation process.

[0089] As shown in FIG. 10B, the luminescent layer 26 includes aplurality of polycrystalline silicon grains 51, a thin silicon oxidefilm 52 formed over the surface of each of the grains 51, the number ofnanocrystalline silicons 63 residing between the adjacent grains 51, anda silicon oxide film 64 formed over the surface of each of thenanocrystalline silicons 63. The silicon oxide film 64 is an insulatingfilm having a thickness less than the crystal grain size of thenanocrystalline silicon 63. It is believed that the remaining region ofthe luminescent layer 26 other than the grains 51, the nanocrystallinesilicons 63 and the silicon oxide films 52, 64 is formed of amorphoussilicon or partially oxidized amorphous silicon. That is, theluminescent layer 26 includes the polycrystalline silicon, and thenumber of nanocrystalline silicons 63 residing around the grain boundaryof the polycrystalline silicon. Each of the grains 51 extends in thethickness direction of the silicon substrate 21.

[0090] The upper electrode 27 is formed of a carbon thin film 27 alaminated on the luminescent layer 26, and a metal thin film 27 blaminated on the carbon thin film 27 a. The carbon thin film 27 a is incontact with the nanocrystalline silicons 63 through the respectivesilicon oxide films 64 formed over the surface of the nanocrystallinesilicons 63. In view of suppressing absorption of light generated in theluminescent layer 26 to prevent the deterioration of optical output, thethickness of the carbon thin film 27 a in the upper electrode 27 is setin the range of 1 nm to 5 nm. Further, the total thickness of the carbonthin film 27 a and the metal thin film 27 b is arranged at about 10 nm.

[0091] For the same reasons as those of the carbon thin film 27 a in thefirst embodiment, the carbon thin film 27 a has excellent compatibilitywith the luminescent layer 26, and high water-repellency. The carbonthin film 27 a can also provide excellent coverage while facilitatingreduction in film thickness, and prevent impurities such as oxygen orwater from being mixed into the luminescent layer 26. In addition, thecarbon thin film 27 a has excellent adhesion with the luminescent layer26 as well as excellent heat resistance and oxidation resistance.

[0092] The material of the carbon thin film 27 a may be selected on thesame basis as that of the carbon thin film 7 a in the first embodiment.In this case, it is understood that the same effects as those in thefirst embodiment can be obtained. Further, if an impurity is doped intothe carbon thin film 27 a to provide a conducting property therein, theelectrical resistance of the carbon thin film 27 a will be reduced.Thus, a required driving voltage and power consumption can be reducedwhile suppressing undesirable affects from heat generation or voltagedrop in the carbon thin film 27 a, as with the carbon thin film 7 a inthe first embodiment.

[0093] The material of the metal thin film 27 b may be selected on thesame basis as that of the metal thin film 7 b in the first embodiment.In this case, it is understood that the same effects as those in thefirst embodiment can be obtained.

[0094] In order to allow the light-emitting device 20 as shown in FIG.10A to emit light therefrom, a voltage may be applied between the upperelectrode 27 and the lower electrode 25. The luminescent layer 26generates light in response to an electric field acting thereon when thevoltage is applied between the upper electrode 27 and the lowerelectrode 25. The light generated in the luminescent layer 26 is emittedoutside after transmitting through the upper electrode 27.

[0095] In the light-emitting device 20 according to the secondembodiment, the upper electrode 27 is formed of the carbon thin film 27a having excellent compatibility with the luminescent layer 26 servingas a base thereof and high water-repellency, and the metal thin film 27b. The carbon thin film 27 a can provide excellent coverage whilefacilitating reduction in film thickness, and prevent impurities such asoxygen or water from being mixed into the luminescent layer 26. Inaddition, the carbon thin film 27 a has excellent adhesion with theluminescent layer 26 as well as excellent heat resistance and oxidationresistance. Thus, the light-emitting device 20 can prevent or suppressthe conventional problems such as the peeling of the upper electrode 27from the luminescent layer 26, the aggregation of the components of theupper electrode 27 and the oxidation of the upper electrode 27.Therefore, as compared to the conventional light-emitting device havingthe upper electrode formed of only the metal electrode, thelight-emitting device 20 according to the second embodiment can haveenhanced durability while suppressing deterioration in optical output.

[0096] With reference to FIGS. 11A to 11D, a production method of thelight-emitting device 20 according to the second embodiment will bedescribed below.

[0097] In the production process of the light-emitting device 20, anohmic electrode 22 is first formed on the back surface of a siliconsubstrate 21. Then, a non-doped polycrystalline silicon layer 23 havinga given thickness (e.g. 1.5 μm) is formed on the principal surface ofthe silicon substrate 21 to provide a structure as shown in FIG. 11A.The non-doped polycrystalline silicon layer 23 may be formed through thesame method as that of the polycrystal silicon layer 3 in the firstembodiment.

[0098] After the formation of the non-doped polycrystalline siliconlayer 23, a nanocrystal layer 24 including a polycrystalline silicon,nanocrystalline silicons and amorphous silicons is formed through ananocrystallization process to provide a structure as shown in FIG. 11B.The nanocrystallization process may be the same as that in the firstembodiment.

[0099] After the completion of the nanocrystallization process, aluminescent layer 26 having the structure as shown in FIG. 10B isobtained through an oxidation process to provide a structure as shown inFIG. 1C. The oxidation process may be the same as that in the firstembodiment.

[0100] After the formation of the luminescent layer 26, a carbon thinfilm 27 a and a metal thin film 27 b are formed in turn. Through thisprocess, an upper electrode 27 in the form of a laminate film formed ofthe carbon thin film 27 a and the metal thin film 27 b is formed on theluminescent layer 26 to provide a light-emitting device 20 having astructure as shown in FIG. 11D. The respective methods of forming thecarbon thin film 27 a and the metal thin film 27 b may be the same asthose of forming the carbon thin film 7 a and the metal thin film 7 b inthe first embodiment, respectively.

[0101] The above production method allows a light-emitting device 20 tobe produced at a high yield rate while suppressing deterioration inoptical output and improving durability.

[0102] In the second embodiment, the luminescent layer 26 includes thesilicon oxide films 52, 64 in addition to the polycrystalline silicongrains 51 and the nanocrystalline silicons 63. However, a siliconnitride film or silicon oxynitride film may be included as a substitutefor the silicon oxide films 52, 64. In this case, instead of theoxidation process, a nitriding process or an oxynitriding process may beused.

[0103] In the second embodiment, the upper electrode 27 is composed ofthe laminate film consisting of the carbon thin film 27 a and the metalthin film 27 b. However, the supper electrode 27 may be formed of onlythe carbon thin film 27 a.

[0104] In the second embodiment, the lower electrode 25 is composed ofthe silicon substrate 21 and the ohmic electrode 22. Alternatively, thelower electrode may be a single-layer or multilayer metal thin film madeof metal and formed on the insulative substrate, as in the firstembodiment.

[0105] In the light-emitting device 20, while the luminescent layer 26includes at least the nanocrystalline silicons 63, the grains 51 are notessentially included therein. In this case, a part of the principlesurface of the silicon substrate 21 may be subjected to thenanocrystallization process and the oxidation process without formingthe polycrystalline silicon layer 23 on the principal surface of thesilicon substrate 21. Further, the silicon oxide films 52, 62 may be notessentially included. In this case, the oxidation process may beomitted, or the silicon oxide films 52, 62 may be removed after theformation of the silicon oxide films 52, 62.

[0106] In the second embodiment, the non-doped polycrystalline siliconlayer 23 is formed on the n-type silicon substrate 21. Instead of thisstructure, an n-type polycrystalline silicon layer may be used as thepolycrystalline silicon layer 23. Alternatively, a p-type siliconsubstrate and a p-type polycrystalline silicon layer may be used as thesilicon substrate 21 and the polycrystalline silicon layer 23,respectively.

[0107] (Example of Second Embodiment)

[0108] A light-emitting device 20 as one example was actually producedin accordance with the production method according to the secondembodiment, and a voltage-current characteristic and electroluminescenceintensity (EL intensity) were measured. The measurement result is shownin FIG. 12. In this example, an n-type silicon substrate having aresistivity of 0.1 Ω cm was used as the silicon substrate 21.

[0109] A non-doped polycrystalline silicon layer 23 (see FIG. 11A) wasformed through a plasma CVD method to have a thickness of 1.5 μm. Thenanocrystallization process was performed by using an electrolyticsolution prepared by mixing a water solution containing 55 wt % ofhydrogen fluoride with ethanol at a ratio of about 1:1. In theelectrolytic solution cooled down to 0° C., a constant current of 25mA/cm² from a power supply was supplied between the lower electrode 25serving as an anode and a platinum electrode serving as a cathode for 8seconds while irradiating the principal surface of the polycrystallinesilicon layer 23 with light by using a 500 W tungsten lump as a lightsource. An electrochemical oxidation process was used as the oxidationprocess. In an oxidation-processing bath containing 1 mol/l of H₂SO₄, avoltage of 27 V was applied between a platinum electrode (not shown) andthe lower electrode 25.

[0110] An upper electrode 27 is a laminate film consisting of a carbonthin film 27 a having a thickness of 2 nm and a gold thin film having athickness of 10 nm which were formed through a sputtering method.

[0111] In FIG. 12 showing characteristics of the light-emitting device20 of this example, the horizontal axis represents a voltage appliedbetween the upper electrode 27 and the lower electrode 25, and thevertical axis on the left side representing a current density of acurrent flowing between the upper electrode 27 and the lower electrode25, and the vertical axis on the right side representing anelectroluminescence intensity. Further, a indicates a dependence of thecurrent density of the current flowing between the electrodes 27, 25 tothe applied voltage, and β indicates a dependence of theelectroluminescence intensity to the applied voltage.

[0112] As seen in FIG. 12, the light-emitting device 20 of this exampleprovided excellent optical output, irrespective of the polarity of thevoltage applied between the upper electrode 27 and the lower electrode25.

[0113]FIG. 13 shows a graph showing respective aging characteristics ofthe current density of the current flowing between the electrodes 27,25, and the electroluminescence intensity. In FIG. 13, the horizontalaxis represents a lapsed time, the vertical axis on the left siderepresenting the current density of the current flowing between theupper electrode 27 and the lower electrode 25, and the vertical axis onthe right side representing the electroluminescence intensity. Further,a indicates an aging characteristic of the current density of thecurrent flowing between the upper electrode 27 and the lower electrode25, and β indicates an aging characteristic of the electroluminescenceintensity. As seen in FIG. 13, the light-emitting device 20 of thisexample provided excellent aging characteristics. While not shown inFIG. 13, the light-emitting device 20 of this example also has excellentaging characteristics in both the current density and theelectroluminescence intensity, as compared to the conventionallight-emitting device having the upper electrode 27 formed of only themetal thin film.

[0114] While the present invention has been described by reference tospecific embodiments, various modifications and alterations will becomeapparent to those skilled in the art. Therefore, it is intended that thepresent invention is not limited to the illustrative embodiments herein,but only by the appended claims and their equivalents.

INDUSTRIAL APPLICABILITY

[0115] As mentioned above, the quantum device according to the presentinvention is useful for providing improved adhesion of the surfaceelectrode with the silicon layer, heat resistance and oxidationresistance as well as enhanced durability, and suitable as electronsources or light-emitting devices.

1. A quantum device comprising: a lower electrode; a silicon layerformed on said lower electrode, said silicon layer including a number ofnanocrystalline silicons to induce a quantum effect in response to anelectric field applied thereto; and a carbon thin film formed on saidsilicon layer to be in contact with the nanocrystalline silicons.
 2. Thequantum device according to claim 1, further comprising a metal thinfilm formed on said carbon thin film.
 3. The quantum device according toclaim 2, wherein said metal thin film is composed of a material selectedfrom the group consisting of gold, platinum, silver, copper, hafnium,zirconium, titanium, tantalum, iridium, niobium, chromium, aluminum, andcarbide or nitride thereof.
 4. The quantum device according to claim 1,wherein said carbon thin film is composed of graphite or graphite-likecarbon.
 5. The quantum device according to claim 1, wherein said carbonthin film has a conducting property yielded by doping an impuritytherein.
 6. The quantum device according to claim 1, wherein said carbonthin film has a thickness of 5 nm or less.
 7. The quantum deviceaccording to claim 6, wherein the thickness of said carbon thin film is1 nm or more.
 8. The quantum device according to claim 1, wherein saidcarbon thin film is a film formed under a temperature of 250° C. ormore.
 9. The quantum device according to claim 1, which is subjected toa heat treatment after said carbon thin film is formed therein andbefore the electric field is applied thereto.
 10. The quantum deviceaccording to claim 2, which is subjected to a heat treatment after saidcarbon thin film and said metal thin film are formed therein and beforethe electric field is applied thereto.
 11. The quantum device accordingto claim 9, wherein said heat treatment is performed at a temperature of380 to 420° C.
 12. The quantum device according to claim 10, whereinsaid heat treatment is performed at a temperature of 380 to 420° C. 13.The quantum device according to claim 1, wherein said silicon layer is astrong electric field drift layer capable of accelerating electronsbased on a strong electric field effect, wherein said quantum deviceserves as an electron source.
 14. The quantum device according to claim13, wherein said silicon layer is a composite nanocrystal layer whichincludes a polycrystalline silicon, and a number of nanocrystallinesilicons residing around the grain boundary of said polycrystallinesilicon.
 15. The quantum device according to claim 1, wherein saidsilicon layer is a luminescent layer capable of generating light inresponse to an electric field applied thereto, wherein said quantumdevice serves as a light-emitting device.